Air cushion restraint systems or inflatable restraints have been in use for several decades in automobiles. These systems have demonstrated their effectiveness in reducing occupant injuries in the event of vehicle impacts. Inflatable restraints are typically used to provide frontal impact protection, and variants are used for protection in side impact conditions. These systems generally incorporate a gas generator, referred to as an inflator, coupled with a flexible fabric bag which is stored in a folded condition and is inflated by the gasses generated by the inflator upon receiving a deployment signal. These devices are stored behind interior compartment panels and are normally hidden from view. Various types of impact sensors are located at strategic locations around the vehicle to detect the deceleration forces associated with a vehicle impact. A restraint system controller receives crash sensor inputs, evaluates them, and sends an appropriate deployment signal to initiate the deployment sequence when the sensors detect a particular crash-type and severity level.
Designers of inflatable restraint systems have made significant advancements in the design and manufacture of such systems. One area of development has been in the design of multiple level inflator systems. These systems incorporate an inflator capable of modulating the volume of produced gas and the deployment timing sequence as needed for a particular category of occupant or type of impact. In order for such systems to properly adapt to the occupant, some type of sensing system is needed to classify the occupant within certain ranges of seating height, mass, etc.
Frontal impact inflatable restraint systems are designed for seated occupants within a given seated height and mass range. Presently available inflatable restraint systems are not intended to provide impact protection for belted child restraints, or for various small sized children occupants. For these particular types of occupants, it is preferred to disable the inflatable restraint system entirely for that designated seating position.
Disabling an inflatable restraint for a given designated seating position may be accomplished through a manual driver input as is currently done with certain presently available vehicles. This approach is primarily provided for two-passenger vehicles where it may be necessary for a driver to place a child restraint seat in the front passenger seat of the vehicle. In such cases, the driver has a keyed switch to disable the inflatable restraint system for that designated seating position. Although such a manual inflatable restraint override switch is effective when used properly, there are concerns both by automotive manufacturers and governmental regulatory authorities that such an approach is cumbersome and unreliable. Improperly used, such systems can result in inappropriate deployment in some instances, and deactivation in conditions where the system could provide impact protection for the seated occupant.
In order to overcome the disadvantages of a manually operated inflatable restraint override switch, manufacturers have investigated and developed a number of technical solutions which automatically evaluate an occupant sitting in a vehicle. Examples of such automated systems include ultrasonic ranging systems which evaluate a sonic return signal as a means of classifying an occupant. Another general category of such occupant classification systems include the use of seat carried sensors. The seats are instrumented with a number of sensors which are activated to produce signals which are interpreted by the inflatable restraint system controller. Such switches may sense pressure, force, displacement, or may be sensitive to an electrical signal parameter such as capacitive coupling. Although such systems have proved effective, there is a continuing need to improve their reliability, ease of assembly, and enable the outputs of the seat sensors to be processed rapidly.